Before we can engage Kaz'Rogal himself we will need to get through the trash waves. Below all the mobs that are in the trash waves are described and explained what they do and how we handle each individual mob. Then a list of wave-setup follows to get a quick overview and feel for how to deal with each wave on its own. After that Kaz'Rogal will follow and below you will find a short description of his abilities and how to deal with each one of them. I have added a picture from Bosskillers to the Kaz'Rogal part of this guide to give an idea on how to spread out.

Trashmobs on Kaz'Rogal

Looking at the waves on Rage Winterchill, Anetheron and Kaz'Rogal theres only a few simple concepts we have to take into account. For the Kaz'Rogal fight we will have Gargoyles and Frost Wyrms joining in. For the mobs I have only listed the abilities that are important to know about during the trash waves.

Ghouls, Abominations and Crypt Fiends
A Hunter kites a Ghoul/Abomination/Crypt Fiend (preferably a Ghoul) towards the NPCs to engage them into the fight, when that is done they kite the mob(s) back through the AoE. The AoE groups consist of Ghouls/Abominations and Crypt Fiends, any class that can AoE will be helping out on these mobs.

Ghoul special ability
Cannibalise - When they go low on health, the Ghouls will run to a corpse and start cannibalizing it, restoring about 7% of their health every 2 seconds, for 10 seconds. If you see a Ghoul cannibalizing, you must stun it or Shackle it or even Fear it as fast as you can to prevent it restoring health. A cannibalizing Ghoul takes an entire raid's worth of DPS to kill.

Abomination special ability
Poison Aura - Sometimes the Abomination will use a poison cloud-like ability, dealing roughly 750 damage to everyone around the Abomination every 3 seconds (basically this is nothing to worry about since only the tanks will get hit and should be healed through).

Crypt Fiend special ability
They will sometimes shoot out tiny spiders at a random person in range. They do about 300-400 damage total. Absolutely nothing to worry about and should just be healed through.

Shadowy Necromancers
A tank picks these up (a DPS Warrior will do), usually there is 1 or 2 alive and kicking so that shouldn't be a problem, anything extra is sheeped/feared. Melee will kill these mobs, it is important that they interrupt their main abilities, which is "Summon Skeletons" and "Shadow Bolt".

Shadowy Necromancer special abilities
Shadow Bolt- A bolt of shadow dealing 2250-2750 to the current target.

Summon Skeletons - Summon a skeleton from a nearby corpse. They can be either a Skeleton Invader, with 32k HP, or a Skeleton Mage with 24k HP. One is a melee type, the other one is a caster. They are no real threat, just an irritation.

Banshees
The Banshees are the mobs to be shackled, depending on the number of mobs we can decide to shackle a few. The Banshees die before the Shadowy Necromancers will, so when there are waves with both the Shadowy Necromancers will be sheeped/feared while melee will focus on the Banshees.

Banshee special abilities
Banshee Curse - Reduces chance to hit by 66% for 5 min. Decurseable.

Banshee Wail - Much like a Shadow Bolt, it causes 2475 to 3025 to the current target.

Anti-Magic Shell - Creates an anti-magic shield around the caster, absorbing up to 200,000 magic damage for 30 seconds. Can be purged.

Gargoyles
The Gargoyles will start in the air, out of melee range. However, if they aggro someone and he goes out of their Gargoyle Strike range, they will land and follow by ground and remain grounded. What we want to do is pull them down to the ground by aggroing them, we can leave this up to 2 Hunters and 2 healers to bring them towards the raid, or we can have all ranged DPS get aggro and move them down to a spot near the Tauren Warriors where they then can be tanked and killed (either AoE or Focus Fire). In both cases melee DPS is taking out the other melee trash.

Gargoyle special ability
Gargoyle Strike - Deals 850 to 1150 nature damage to an enemy. The spell has a 35 yard range and a 1.5 second cast.

Frost Wyrms
They will remain airborne until they die, and so cannot be damaged by melee. They will come in waves 6 and 7 from the direction of the 2 Towers where the tanks and Shadowy Necromancer DPS are. Have him off tanked by a Hunter, Mage or Warlock somewhere away from people, these mobs get killed by ranged DPS.

Frost Wyrm special ability
Frost Breath - A 3 second cast, 35 yard range ability that deals 2550 to 3450 frost damage to it's target and everyone in 8 yards around it, and slowing their movement speed by 50% for 6 seconds.

Waves on Kaz'Rogal

Wave 1 - 4 Ghouls, 4 Abominations, 2 Banshees, 2 Shadowy Necromancers.
Wave 2 - 4 Ghouls, 10 Gargoyles
Wave 3 - 4 Ghouls, 6 Crypt Fiends, 4 Shadowy Necromancers
Wave 4 - 6 Gargoyles, 6 Crypt Fiends, 2 Shadowy Necromancers
Wave 5 - 4 Ghouls, 6 Abominations, 4 Shadowy Necromancers
Wave 6 - 8 Gargoyles, 1 Frost Wyrm
Wave 7 - 6 Ghouls, 4 Abominations, 1 Frost Wyrm
Wave 8 - 6 Ghouls, 2 Crypt Fiends, 6 Abominations, 2 Banshees, 2 Shadowy Necromancers,

Wave 9 - Boss - Kaz'Rogal will come from the same area that all the waves came from. He'll walk slowly until he finds a target to engage, if all the mobs in the front are already dead. Otherwise, he'll kill them first.

Kaz'Rogal

HP - 4,200,000
Melee Strength - 2000-3000 on plate.

Cleave
Kaz'rogal has a frontal cleave that hits a well geared tank for up to 10,000, but can hit anyone else for a lot more.

Mark of Kaz'Rogal
Kaz'Rogal places a debuff on everybody in the raid, called Mark of Kaz'Rogal. It has no effect on non-mana users. On everyone else, it drains 600 mana every second for 5 seconds for a total of 3000 mana. If you don't have any mana to drain, you will detonate for 10213 to 11287 shadow damage in a 10-15 yard area around you.

War Stomp
Periodically uses this ability, dealing 2313-2687 damage to everybody in a 15 yards radius of him, stunning them for 5 seconds. Does not cause the MT to lose aggro.

Dispel
Randomly dispels one magic effect from a player.

How to do deal with each ability
Melee Attacks
He doesn't hit that hard for a boss, however the Cleave will add substantial extra damage which needs to be healed fast.

Cleave
As said above, the Melee Attacks on their own are not that harmful, the Cleave however is dangerous and so healers must pay extra attention to the tank. My guess is 3-4 dedicated MT healers should be enough to heal his Melee Attacks and Cleaves, however more healers is better as it will save Mana in the long run.

Mark of Kaz'Rogal
If the Mark runs you out of mana and detonates, you will take considerably less damage if you have some mana to be drained than if it hits you on empty, so make sure you always have *some* mana. It is vital though that healers and ranged DPS should try not get below 4000 Mana, everyone should do everything to prevent them from going below 3000 Mana.
Any SR gear will help counter both the damage done by the mark but also the mark itself, so anyone that has some SR gear should wear about 200 (as a maximum) for this encounter, it is not needed but it will make it so much easier for everyone.
Another important countermeasure to take in case someone does detonate is spreading, try and spread out about 15y from each other so the detonation does not hit you when the player next to you detonates.

War Stomp
Because Kaz'rogal is so enormous, and his hitbox is too, it is actually possible for melee to hit him whilst standing out of range of this ability, so melee should try this. The tank can just keep on tanking, as long as DPS does not overaggro in the 5 seconds the MT is stunned.

Dispel
Nothing to worry about, just annoying!

Extra

It is important that we spread out enough, other then that positioning is not that important. It is smart to pull aggro on Thrall and possibly the Tauren Warriors as they deal a good amount of damage on the boss and every little bit helps.